Thanks sandman ,
could you explain the point of ground balance?
so which one of these do you prefer minelab x terra 305,teroso cibola,f4, whites coin master pro?
On another note which of these have the best depth reading? (how do i figure it out ) Or does it really just depend on conditions ?
Basically Ground Balance calibrates the MD so that it doesn't see the mineralization in the soil. With the machine not spending time on the false signals this can cause, and static, you'll get smoother operation and better signals.
One thing to look into before buying a used machine is to make sure it's still supported by the factory. If not and the machine breaks down, then you couldn't get it repaired.
As many people buy MD's and then give it up after they find out how much work it is, and after how much trash you'll dig, relegate the machine to the back of the closet. So there are great bargains to be had. In fact I saw a Whites D6000 (I'm pretty sure that's the right model) being pawned and it looked like it had never seen dirt.
With the invention of the net, most manuals for any machine you'd be looking at is likely to be online. That's great information to read beforehand.
If you have a dealer nearby, or within reasonable driving distance, give them a visit. You'll be able to look at new and used machines and see which one fits you. And by dealer, I don't mean a box store that has one section dedicated to md"s.
If buying new give serious consideration to Tesoro...the lifetime warranty is unbeatable. (Yes, I love my Tesoro.)
As Sandman said stick with the major brands and you should be happy. If you budget allows it go with at least a mid-level machine or higher.